Such a flexible pipe is for example made according to normative documents API 17J (Specification for Unbonded Flexible Pipe) and API RP 17B (Recommended Practice for Flexible Pipe) established by the American Petroleum Institute.
The pipe is generally formed by a set of concentric and superimposed layers. It is considered “unbonded” within the meaning of the present invention when at least one of the layers of the pipe is able to move longitudinally relative to the adjacent layers when the pipe is bent. In particular, an unbonded pipe is a pipe with no bonding materials connecting the layers forming the pipe.
The pipe is generally positioned through an body of water, between a bottom assembly, designed to collect the fluid produced in the bottom of the body of water, and a floating or stationary surface assembly designed to connect and distribute the fluid. The surface assembly may be a semisubmersible platform, an FPSO or another floating assembly.
In some cases, the flexible pipe comprises an inner carcass positioned in the pressure sheath, in order to avoid crushing of the pressure sheath under the effect of the external pressure, for example during depressurization of the inner fluid circulation passage defined by the pressure sheath.
The inner carcass is generally formed by a profiled metal tape, wound in a spiral. The turns of the tape are interlocked to one another. The turns define a helical interstice between them emerging radially inwardly in the central circulation passage of the fluid.
The inner surface of the carcass therefore axially has a series of hollows and bumps. The pipe is then designated by the term “rough bore”.
In some cases, the circulation of the fluid along the carcass is disrupted by the reliefs defined on the carcass by the helical interstice.
This disruption of the flow is sometimes considered to be the source of vibration phenomena within the flexible pipe, or even, when a resonance is reached, of flow-induced pulsations (or “singing”).
To offset this problem, it is known to manufacture flexible pipes with no inner carcass and therefore having a smooth surface (“smooth bore”).
Another solution to this problem is described in WO 2014/000816. In this document, the flexible pipe comprises a carcass in which a helical insert with a T-shaped cross-section is jammed in the interstice present between the different turns of the carcass. The insert inwardly plugs the interstice.
The T-shaped profile is manufactured from two planar tapes, for example by welding between the tapes.
The manufacture of such an insert, and its arrangement in the carcass, is therefore very difficult to implement industrially.
In particular, the assembly by welding of two tapes requires implementing major equipment on the line, such as unwinders, an assembler, a laser welding station, etc.
Alternatively, the T-shaped profile could be manufactured upstream from the production of the carcass and can be stored on a drum. However, storing the T-shaped profile on a drum causes certain problems.
First of all, the shape of the profile makes it difficult to store and unwind, in particular due to the risk of “drag marks”.
Furthermore, it is necessary to have a large inventory of drums, which increases costs, complicates handling, and requires a large storage area.
It is also necessary to provide a specific welder during reloading and leveling of the profile.